SILICATES, TITANATKS, I ,T< 



A massive variety has been described from Tehama County, 



( ';ililorni:i, :md Alaska. 



WOLLASTONITE 



Wollastonite. Calcium metasilicate, CaSiOa ; CaO = 48.3, 

 SiO 2 = 51.7; Monoclinic ; Type, Digonal E(iuatorial ; a:b:c = 

 1.0531 : 1 : .9676; P = 84 30' == 100 A 001; 100 A 110 = 46 

 2 1 ' ; 001 A 101 == 45 5' ; 001 A Oil == 43 55' ; Common forms, 

 c(001), a (100), h(540), m(110), v (101) ; Twinning plane, 100; 

 Cleavage, a perfect, c less so; Brittle; Fracture, uneven; H. = 

 4.5-5 ; G. = 2.8-2.9 ; Color, white, gray, yellow, brown, or pink ; 

 Streak, white ; Luster, vitreous to pearly ; Translucent to opaque ; 

 a = 1.621; p = 1.633; v = 1 - 63 5; -Y = a = .014; Optically 

 (-); Axial plane = 010; Bx aA c = 32 12' behind; 2E=70. 



B.B. Fuses quietly to a white, somewhat glassy globule. Gelat- 

 ini/es \vith HC1 ; the solution freed of silica yields little or no 

 precipitate with ammonia, but a heavy white precipitate with 

 ammonium carbonate (calcium). 



General description. In habit crystals are tabular, with the 

 base as the prominent face, or elongated parallel to the orthoaxis ; 

 also fibrous or divergent, but usually in cleavable masses. The 

 color is white to gray in pure material, but as iron and manganese 

 replace the calcium the color becomes brown or pink. 



Wollastonite is a characteristic mineral of contact metamorphic 

 regions where there is an abundance of calcium ; it is therefore a 

 common mineral in crystalline limestones, where it is associated 

 with garnets, epidote, vesuvianite, diopside, etc. It may occur in 

 lavas and basalts, where it is associated with nepheline. 

 A pink variety containing considerable manganese occurs at 

 Franklin, New Jersey. Wollastonite also occurs at various places 

 in Lewis County, New York, in well-formed crystals; in the Lake 

 Superior region, and at Grenville, Quebec. 



There are two forms of calcium metasilicate ; the /J-CaSiOs is 

 stable below 1190. This form is the mineral Wollastonite. The 

 other form, a-CaSiOs, is pseudo-hexagonal, is the stable form above 

 1190, and is formed when the constituents are fused in an open 

 crucible and cooled quickly. It is the common form of calcium 

 metasilicates found in slags. Wollastonite is formed when a glass 

 of the composition of CaSiO 3 is heated to 900 or 1000 and kept 



